Optical absorption spectrum of Ni2+ ion doped in synthetic lecontite

The optical absorption spectrum of Ni²⁺ ion doped in lecontite (sodium ammonium sulphate dihydrate) single crystal has been studied at room and liquid air temperatures. All the bands could be assigned assumingO _h symmetry for the Ni²⁺ ion in the crystal. The splitting of³ T _1g (F) band at liquid air temperature has been attributed to spin-orbit interaction. The crystal field and spin-orbit parameters derived areD _q=1000 cm^?1;B=740 cm^?1;C/B=4.27 and ζ=600 cm^?1. All the bands observed show a blue shift when the crystal was cooled to liquid air temperature.     

Resonant two-photon absorption in the Cr2O3 antiferromagnet

Two-photon absorption (TPA) spectra of the Cr₂O₃ model antiferromagnet have been studied for two polarization configurations at energies ranging from 2.5 to 3.55 eV. Several strong TPA peaks with the maximum coefficient β ～ 0.08 cm/MW are observed in the 2.7–3.1-eV range characterized by the ⁴ A ₂(F) → ⁴ T ₁(F) d-d one-photon transition of the Cr³⁺ ion. An analysis of the results obtained suggests that the general form of the TPA spectrum in this range is primarily determined by the resonance at the ² E(G) and ² T ₁(G) intermediate levels. At energies above 3.44 eV, the TPA coefficient sharply increases up to β ～ 0.1 cm/MW due to transitions between the valence and conduction bands.     

Electron paramagnetic resonance and photoluminescence properties of α-Al2O3:Cr3+ phosphors

The red emitting Cr³⁺ activated α-Al₂O₃ powder phosphor has been prepared by easy combustion reactions from mixed metal nitrate reactants and urea with ignition temperatures of 500 °C. The as-synthesized powder was characterized by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared techniques. The X-ray diffraction pattern reveals that the phosphor crystallized in the hexagonal α-Al₂O₃ phase directly from the combustion reaction. The EPR spectrum exhibits an intense resonance signal with effective g value at g=3.33 along with a few weak resonance signals with effective g values at g=13.7, 2.34, 1.95, 1.49, and 1.26. The spin concentration (N) and its paramagnetic susceptibility (χ) have been evaluated. The excitation spectrum consists of two broad intense bands at 415 nm and 555 nm and are assigned to ⁴A_2g (F)→⁴T_1g (F) and ⁴A_2g (F)→⁴T_2g (F) transitions, respectively. The intense fluorescence peak around 691 nm is attributed to ²E _g →⁴A_2g transition of Cr³⁺ ion. By correlating EPR and optical data, the crystal field splitting parameter (Dq), Racah inter-electronic repulsion parameter (B) have been evaluated and discussed. The EPR and optical studies reveal that Cr³⁺ ions are occupying in Al³⁺ sites in octahedral coordination.     

Ab initio and crystal field studies of the Mn4+-doped Ba2LaNbO6 double-perovskite

A detailed study using the ab initio DFT-based calculations of the electronic and optical properties of pure and Mn⁴⁺ doped Ba₂LaNbO₆ is presented in this paper. Comparison of the calculated electronic bands structure, density of states diagrams, and dielectric functions for the pure and doped crystal reveals the changes induced by the Mn⁴⁺ impurity ions. In addition, the energy levels of the Mn⁴⁺ ion in the ordered perovskite Ba₂LaNbO₆ are calculated by the exchange charge model (ECM) of crystal field theory and compared with the experimental data that has been presented in the literature. The calculated Mn⁴⁺ energy levels are in good agreement with the experimental spectra. Additionally, the excitation band shapes of the ⁴A_2g(⁴F)–⁴T_2g(⁴F) and ⁴A_2g(⁴F)–⁴T_1g(⁴F) transitions are modeled to estimate the zero-phonon lines (ZPL) positions and the effective number of phonons, which are involved in the corresponding excitation transition. The results of our calculations yield the crystal field parameter of Dq=1780 cm^?1 and Racah parameters B=670 and C=3290 cm^?1, with C/B=4.9 for the Mn⁴⁺ ion in the double-perovskite Ba₂LaNbO₆.     

Absorption spectrum of Cr3+ ion doped in lithium ammonium sulphate single crystal

The absorption spectrum of Cr³⁺ ion doped in lithium ammonium sulphate single crystal has been studied both at room (300 K) and liquid nitrogen (77 K) temperatures. From the nature and position of the observed bands, O_h symmetry is assumed for the ion. The spectroscopic parameters derived for the ion in the crystal at 77 K are Dq = 1655 cm^?1, B = 735 cm^?1 and C/B = 4.4     

EPR and Optical Absorption Study of Cr3+-Doped Dipotassium Tetrachloropalladate

X-band electron paramagnetic resonance (EPR) study of Cr³⁺-doped dipotassium tetrachloropalladate single crystal is done at liquid nitrogen temperature. EPR spectrum shows two sites. The spin-Hamiltonian parameters have been evaluated by employing hyperfine resonance lines observed in EPR spectra for different orientations of crystal in externally applied magnetic field. The values of spin-Hamiltonian and zero-field splitting (ZFS) parameters of Cr³⁺ ion-doped DTP for site I are: g _x  = 2.096 ± 0.002, g _y  = 2.167 ± 0.002, g _z  = 2.220 ± 0.002, D = (89 ± 2) × 10^?4 cm^?1, E = (16 ± 2) × 10^?4 cm^?1. EPR study indicates that Cr³⁺ ion enters the host lattice substitutionally replacing K⁺ ion and local site symmetry reduces to orthorhombic. Optical absorption spectra are recorded at room temperature. From the optical absorption study, the Racah parameters (B = 521 cm^?1, C = 2,861 cm^?1), cubic crystal field splitting parameter (Dq = 1,851 cm^?1) and nephelauxetic parameters (h = 2.06, k = 0.21) are determined. These parameters together with EPR data are used to discuss the nature of bonding in the crystal.     

Optical absorption spectrum of Ni2+ ions doped in sodium potassium sulphate single crystal

Single crystals of nickel-doped sodium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the observed bands could be made assuming the octahedral symmetry for the Ni^{2 +} ion in the crystal. The bands have been ascribed to transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The experimental and calculated energies are in good agreement. The crystal field parameters derived areDq= =880 cm^–1,B= 900cm^–1 andC=3600 cm^–1.One of the authors, Sujatha John expresses her thanks to the Secretary and the Principal, R. B. V. R. Reddy College, Hyderabad for according her permission to pursue the M. Phil. course.     

Electronic absorption spectra of the 5d3 hexafluororhenate(IV) ion

The Γ₈(⁴A_2g) →Γ₇(²T_2g), Γ₈(²T_2g) electronic transitions for the 5d³ hexafluororhenate(IV) ion have been observed at liquid hydrogen temperature in a single Cs₂GeF₆ crystal and in a mixed crystal where the ReF^?2₆ ion is doped in the cubic Cs₂GeF₆ lattice. The electronic transitions have been assigned with a crystal field model to give information about the parameters B, C, Dq, and spin-orbit coupling. The vibrational structure in the mixed crystal system may be assigned to the ungerade modes of the ReF^?2₆ moiety. Comparison of the mixed and pure crystal vibrational structure shows that the pure crystal vibrational structure can be interpreted on the basis of K ≠ 0 lattice effects and a small distortion in the pure crystal.     

Electronic absorption spectrum of Ni2+ in lithium potassium sulphate single crystal

Single crystals of nickel-doped lithium potassium sulphate were grown by slow evaporation method at room temperature. From the nature and position of the bands observed, a successful interpretation of all the bands could be made assumingO _h symmetry for the Ni²⁺ ion in the crystal. The bands have been assigned transitions from the ground³A_2g(F) state to the excited³T_2g(F),¹E_g(D),³T_1g(F),¹T_2g(D) and³T_1g(P) states. The crystal field parameters derived areDq=910cm^–1,B=890cm^–1 andC=3560cm^–1.The authors wish to express their thanks to Prof. K. Sreerama Murthy for his constant encouragement throughout this investigation. The authors are also thankful to Prof. Mihir Chowdhury, Indian Association for the cultivation of Science, Calcutta for giving permission to take the spectra.     

Excitation spectra and fluorescent lifetime measurements of Mn2+ in CaF2 and CdF2

The excitation spectrum of the Mn²⁺ emission has been measured in CaF₂ and CdF₂. The observed excitation bands have been assigned to transitions of the Mn²⁺ ions in a cubic environment. The calculated values for the crystal field (Dq) and Racah parameters (B,C) are Dq = 425 cm^-1 for CaF₂, Dq = 500 cm^-1 for CdF₂ and, B = 770 cm^-1 and C / B = 4.48 for both compounds. The lifetime of the fluorescent level ⁴T_1g(⁴G) has been measured in both compounds at different temperatures in the range from 10 to 500 K. The lifetime thermal dependence is explained taking into account different mechanisms (purely radiative, phonon assisted, and radiationless transitions) for the decay of excited Mn²⁺ ions.     

EPR, Optical Absorption and Superposition Model Study of Fe3+-Doped Ammonium Dihydrogen Phosphate Single Crystals

X-band electron paramagnetic resonance (EPR) studies are carried out on Fe³⁺ ions doped in ammonium dihydrogen phosphate (ADP) single crystals at room temperature. The crystal field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations. The obtained values of spin Hamiltonian and zero-field parameters of the Fe³⁺ ion in ADP are: g = 1.994 ± 0.002, |D| = (220 ± 5) × 10^?4 cm^?1 and a = (640 ± 5) × 10^?4 cm^?1. On the basis of EPR data, the site symmetry of the Fe³⁺ ion in the crystal is discussed. The Fe³⁺ ion enters the lattice substitutionally replacing the NH₄ ⁺ sites. The optical absorption of the crystal is also studied at room temperature in the wavelength range of 195–925 nm. The energy values of different orbital levels are calculated. The observed bands are assigned as transitions from the ⁶ A _1g (S) ground state to various excited quartet levels of the Fe³⁺ ion in a cubic crystalline field. From the observed band positions, Racah interelectronic repulsion parameters (B and C), cubic crystal field splitting parameter (D _q ) and Trees correction are calculated. There values are: B = 970, C = 1,923, D _q  = 1,380 cm^?1 and α = 90 cm^?1, respectively. On the basis of EPR and optical data, the nature of bonding in the crystal is discussed. The zero-field splitting (ZFS) parameters are also determined theoretically using B _kq parameters estimated from the superposition model. The values of ZFS parameters thus obtained are |D| = (213 ± 5) × 10^?4 cm^?1 and |E| = (21 ± 5) × 10^?4 cm^?1.     

An IR spectroscopic study of liquid ozone and ozone dissolved in liquid argon

We have measured and interpreted the IR spectra of liquid ozone films at 78–85 K and ozone dissolved in liquid argon at 91–95 K. A less hindered rotation of ozone molecules in argon manifests itself as an intensity redistribution, caused by the Coriolis interaction, from the states ν₃(B ₁) and ν₁ + ν₃(B ₁) to the states ν₁(A ₁) and 2ν₁(A ₁), respectively. The occurrence of wings in the contours of the bands ν₁(A ₁), 2ν₁(A ₁), and 2ν₃(A ₁) in liquid Ar and their absence in the spectrum of O₃ also confirms the conclusion that the rotational motion of ozone molecules in an inert solvent at low temperatures is relatively less hindered. Maxima of ozone bands in Ar solution are shifted toward lower frequencies compared to those in the gas phase by 1–30 cm^?1, which corresponds to the following shifts of harmonic frequencies of the molecule: Δω₁ = ?1.85(5) cm^?1, Δω₂ = ?0.67(7) cm^?1, Δω₃=?7.20(5) cm^?1. It was found that the absorption band of the ν₃ mode in the spectrum of O₃ in the liquid phase has a complicated asymmetric contour because of the resonance dipole-dipole interaction. The first and second spectral moments of this band have been determined to be M ₁ = 1030.6 cm^?1 and M ² = 240.0 cm^?2.     

Hopping conductivity of carbynes modified under high pressures and temperatures: Galvanomagnetic and thermoelectric properties

The conductivity, thermopower, and magnetoresistance of carbynes structurally modified by heating under a high pressure are investigated in the temperature range 1.8–300 K in a magnetic field up to 70 kOe. It is shown that an increase in the synthesis temperature under pressure leads to a transition from 1D hopping conductivity to 2D and then to 3D hopping conductivity. An analysis of transport data at T ≤ 40 K makes it possible to determine the localization radius a ～ (56?140) Å of the wave function and to estimate the density of localized states _g(E _F) for various dimensions d of space: _g(E _F) ≈ 5.8 × 10⁷ eV^?1 cm^?1 (d=1), _g(E _F) ≈5×10¹⁴ eV^?1 cm ^?2 (d=2), and _g(E _F)≈1.1×10²¹ eV^?1 cm_?3 (d=3). A model for hopping conductivity and structure of carbynes is proposed on the basis of clusterization of sp ² bonds in the carbyne matrix on the nanometer scale.     

Optical and electrical characterization of cadmium selenide doped with cobalt

The optical and electrical properties of Co²⁺ ions in CdSe have been investigated. Absorption, photoluminescence, electron paramagnetic resonance, and Hall measurements were used to characterize a cobalt-doped (1×10¹⁹ cm⁻³) single crystal. Infrared absorption and emission spectra associated with transitions between the ⁴A₂(F) ground state and the ⁴T₁(F) and ⁴T₂(F) excited states are described. At 10 K, spin-orbit splittings result in three structured absorption bands associated with the ⁴A₂(F) to ⁴T₁(F) transition having zero-phonon lines at 4926, 5101, and 5724 cm⁻¹. The ⁴A₂(F) to ⁴T₂(F) transition shows two zero-phonon lines at 2874 and 3286 cm⁻¹, also accompanied by vibronic structure. Intrinsic lattice modes explain most of the sharp-line structure observed at low temperature, except for a subset of peaks where local modes (25-30 cm⁻¹) are invoked. Using below-band-gap light, selective excitation allows detection of the ⁴T₁(F) to ⁴A₂(F) recombination at liquid-helium temperatures. The activation of free carriers in our n-type material containing shallow donors is affected by the presence of cobalt, and we find the Co^+/++ level to be about 34 meV below the conduction band of CdSe.     

Spin relaxation of charged centers in silicon in the presence of photocarriers (Si: Cr+, [Cr+−B−])

Spin relaxation of deep charged centers Cr⁺ and of donor-acceptor pairs (Cr⁺?B^?)⁰ in silicon is studied by nonstationary EPR spectroscopy at liquid-helium temperatures. We observed the effect of an increase in the spin-lattice relaxation rate under band-to-band sample illumination; the magnitude of the effect is proportional to the photoelectron concentration. The spin-dependent carrier trapping is shown to play a dominant role in spin relaxation under illumination for centers of both types. Coupled rate equations describing the interaction of various subsystems with one another and with the bath are solved. A comparison of experimental data with theory yielded the electron trapping cross sections σ_r(Cr⁺)?4.9×10^?12 cm² and σ_r(Cr⁺?B^?)?1.6×10^?12 cm² at T=4.2 K. The results obtained are discussed in terms of the theory of trapping by attractive centers.     

Exciton-magnon interactions in NicMg1−c O single crystals

The effect of chemical composition and temperature on exciton-magnon interactions in Ni_cMg_1?c O single crystals was studied using optical absorption spectra in the region of the magnetic-dipole ³ A _2g (G)→³ T _2g (F) and electric-dipole ³ A _2g (F)→¹ E _g (D) transitions. The two zero-phonon lines at ～7800 and ～7840 cm^?1 on the low-energy side of the magnetic-dipole transition band were assigned to a pure exciton transition and an exciton-one-magnon transition at the center of the Brillouin zone. The intensity of the exciton-one-magnon peak decreases rapidly with increasing magnesium ion concentration and/or temperature, to vanish altogether at T=6 K for c<0.95 and at T=130 K for c≥0.99. Thus, the contribution of long-wavelength magnons in optical absorption spectra of Ni_cMg_1?c O becomes negligible at temperatures substantially lower than the Néel point T _N (the antiferromagnetic ordering temperature). This observation can be explained as being due to a substantial decrease in the characteristic spin-spin interaction length with increasing concentration of the diamagnetic magnesium impurity ions (static disorder) and/or with increasing amplitude of thermal atomic vibrations (dynamic disorder). At the same time, the peak at ～14500 cm^?1, which lies in the electric-dipole transition region and corresponds to excitation of an exciton and two magnons at the Brillouin zone edge, remains visible up to the Néel temperature. This is accounted for by the short-wavelength magnons being sensitive to short-range magnetic order, which persists up to T _N .     

Light induced charge transfer processes in Cr doped Bi12GeO20 and Bi12SiO20 single crystals

Optical absorption and ESR spectra of Bi₁₂GeO₂₀ doped with Cr were measured before and after illumination with visible light. It was found that Cr⁴⁺ ions in tetrahedral position are responsible for light induced ESR and optical spectra. The g-factor of the center is 1.945 ± 0.002. Crystal field parameters for the Cr⁴⁺ center are D_q = 820 cm^?1 and B = 429cm^?1. The photochromic effect is explained in terms of a Cr⁵⁺?Cr⁴⁺ charge transfer process.     

Optical absorption spectrum and crystal field of erbium aluminum garnet (ErAlG)

The optical absorption spectrum of Erbium Aluminum Garnet (ErAlG) has been measured between 12000 cm^?1 and 26000 cm^?1. The crystal field splitting of the terms⁴I_15/2,⁴I_9/2,⁴F_9/2,⁴S_3/2,²H_11/2,⁴F_7/2,⁴F_5/2,⁴F_3/2,²H_9/2 and⁴G_11/2 was determined from the spectra and has been analysed in terms of the usual parametrization scheme. Nine crystal field parametersA _l ^m 〈r ^l〉≡B _l ^m which are necessary to describe the crystal field with the symmetryD ₂ at the site of the rare earth ion, were fitted to the experimental data. The values are (in cm^?1):B ₂ ⁰=+160B ₄ ⁰=?160B ₆ ⁰=+30B ₆ ⁶=+80B ₂ ²=?100B ₄ ²=+140B ₂ ⁶=?40B ₄ ⁴=?1800B ₆ ⁴=?700 This result is compared with those obtained from similar analysis of other garnets.     

Electronic Absorption Spectrum of Fe3+ Doped in Ammonium Perchlorate Single Crystal

Abstract

Single crystals of Iron - doped ammonium perchlorate were grown at room temperature. The electronic absorption bands observed at room and liquid air temperatures have been assigned transitions from the ground ⁶A_1g state to the excited ⁴A_1g, ⁴E_g, ⁴T_1g and ⁴T_2g states. The crystal field parameters Dq = 870 cm^?1, B = 615 cm^?1 and C = 4.2 B are found to give a good fit to the observed band positions.     

Fluorescence spectra of matrix-isolated Se2

Laser induced fluorescence spectra are reported for samples of natural selenium and of the separated ⁷⁸Se and ⁸⁰Se isotopes in Ar and Kr matrices. The B(0_u⁺) → X(0_g⁺) and B(1_u) → X(1_g) systems of Se₂, already known in the gas, are observed by both single photon and biphotonic excitation considerably red-shifted in the matrices. The A(0_u⁺) → X(0_g⁺) emission of Se₂, not observed in the vapor, appears in the matrices with its origin near 15 100 cm^?1. Another system with ν₀₀ = 24 429 cm^?1 and ω″_e = 538 cm^?1 is thought to belong most probably to some polyatomic Se_n molecule.